It's not a duplicate, because this question isn't about shredding files that already deleted, it's about deleting them in the first place in a way that recovery software wouldn't find it.
I delete photos, but this software FindMyPhoto still recovers them. I think photos are really deleted, and those that restored are thumbnails, because when I restore them they doesn't look that sharp. I delete photos through the Gallery application. I tried to clean Gallery app cache, that doesn't help.
I tried to use firmware (preinstalled by manufacturer) that cleans Android of junk (like cache etc), but the application above still finds it. And I don't know how to completely remove the files. It's like I've got a device with undeletable files and starting really hate Android (it's really betrayal and annoying behavior).
So if you could recommend some application may be (preferably from a well known company or free software, like those from F-Droid repository) I would appreciate it. Thanks.